If you are talking about D&D and are using the D&D 5E (2014) character sheet, there's no reliable way to automatically have that filled in. I also use one of the token bubbles to list Passive Perception and have to fill it in manually for each NPC. You can try setting it up through the "Game Settings" page that is accessible through your game's start page (see screen shots below) and putting passive_wisdom or npc_perception in the BAR <number> LINK field, but the results won't be consistent. I use passive_wisdom because it is consistent for PC character sheets but not NPC sheets. Some NPC character sheets use one, the other, or neither, some will only give you only the modifier ,and some will give you nothing. This has to do with how the NPC stat blocks are filled out within the compendiums, and the responsibility for that is with the either the publisher or whoever created the compendium from the published data.
